1. Technical Field
The present invention relates to a bias estimating method, a posture estimating method, a bias estimating device, and a posture estimating device.
2. Related Art
In various fields of so-called seamless positioning, motion sensing, posture control, and the like, inertial sensors have attracted attention. An acceleration sensor, a gyro sensor, a pressure sensor, a geomagnetic sensor, and the like are widely known as such inertial sensors.
In recent years, sensor modules equipped with a multiple-axes (multi-axis) inertial sensor have been developed. The multi-axis sensor module is provided with inertial sensors mounted on plural orthogonal axes and is configured to perform a sensing operation in a three-dimensional space. However, there is a problem in that the output of the inertial sensor contains a misalignment error due to the inaccurate attachment of the inertial sensors to the sensor module.
In view of this problem, for example, JP-A-10-267651 discloses a technique of calculating different-axis sensitivity in a multi-axis acceleration sensor and correcting the misalignment error contained in the detection value of the acceleration sensor.
According to the technique disclosed in JP-A-10-267651, the misalignment error can be satisfactorily corrected. However, the output of the acceleration sensor may typically contain a bias component called a zero bias. It is known that a bias (so-called turn-on bias) is created at the time of turning on an inertial sensor, and the bias has a random drift characteristic that it randomly varies with the passage of time.
In recent years, an MEMS (Micro Electro Mechanical System) sensor as a small and inexpensive inertial sensor employing the fine processing technology of semiconductor has been provided to various consumer products. In the MEMS sensor, a mechanical part detecting an inertial force and a conversion part converting the inertial force into an electrical signal are formed on a single silicon wafer by the use of the fine processing technology.
The MEMS sensor has merits such as small size, small weight, low cost, and low power consumption, but has a demerit that it can be easily affected by external influences such as impact, vibration, and temperature variation. The external temperature variation has a great influence on the output of the inertial sensor. A temperature compensation technique of removing a temperature-dependent component from the output of the inertial sensor has also been devised. However, even when the temperature compensation is carried out, there is a problem in that the bias value contained in the output of the inertial sensor is not zero but has a considerable magnitude due to the turn-on bias or external influences other than temperature variations.